In computer systems including integrated circuits, booting is performed to bring up and run operating systems that control the execution of computer programs and provide various services. The boot operation may be categorized as either a cold boot or a warm boot depending on a power condition. For example, for a cold boot, the operating system may be restarted by turning the power on from a power off condition, whereas for a warm boot, the operating system may be restarted without turning the power off.
Semiconductor memory devices may include various circuits, for example, a power-up signal generator that is used to assist with the powering up of the semiconductor memory device. The semiconductor memory device may be operated by an external power supply, and a voltage level of the external power supply may rise from a ground voltage to a target voltage with a certain slew rate. In some cases when the external power supply voltage is directly applied to the circuits of the semiconductor memory device, the semiconductor memory device may malfunction due to a fluctuation of the voltage level outputted from the external power supply. Thus, in order to prevent malfunction of the semiconductor memory device, a power-up signal from a power-up signal generator can be used to apply a stable power supply voltage to the circuits of the semiconductor memory device.